For reference:
Tieflings
Carrying the taint of evil in their very souls, tieflings are persecuted and feared in most parts of Faerûn. Those with gross physical alterations are often killed at birth, and even those with less noticeable physical traits are sometimes killed by their own horrified parents. Occasionally a tiefling is born to someone indifferent to its appearance, determined to redeem it, willing to exploit it, or evil enough not to care about its nature, and these tieflings are most likely to survive to adulthood. Most tieflings are evil, but a few have managed to overcome their bloodline’s influence to make their own choices about good and evil.
Tieflings are the distant descendants of a human and some evil outsider, such as a demon (usually a marilith or succubus), devil (usually an erinyes, gelugon, or pit fiend), night hag, rakshasa, or even a servant of an evil deity (some of these creatures must use magic to assume a form that is compatible with a human mate, of course).
Tieflings live as outcasts. Feared for their evil heritage and often acting appropriately to their ancestry, they learn to keep people at a distance and hide that which makes them different. Like all the planetouched, they are different from their own parents; rarely has a tiefling been raised in a home filled with love. Tieflings are bitter folk who expect eventual rejection from even their best friends and easily fall into lives of crime, depravity, and cruelty. Tieflings look upon true fiends and other evil outsiders with envy and fear.
Some tieflings reject their tainted blood and seek the light. Not many succeed for long, and far more slide to a comfortable place midway between evil and good. But of the creatures who work to be good, good-aligned tieflings probably work the hardest.
Aasimaar
Most aasimar are wary of their human neighbors. Even those raised by parents who understand their heritage cannot escape the stares of other children and adults, for humans fear that which is different. Aasimar usually experience a great deal of prejudice, which is all the more painful to the good-inclined aasimar who truly wants to help others survive in a hostile world. Aasimar are often seen as aloof, when in many cases this is a protective measure born of years of misunderstandings.
Although aasimar are mostly human, they rarely feel like they fit in among human society. Instead, they get along best with other halfbreeds - namely, half-elves and half-orcs - because they and aasimar share the same sort of semi-outcast background.
Dwarves, elves, gnomes and halflings are neither embraced nor shunned by aasimar, for while these races have no history of persecuting the planetouched, they don't have a reputation for sheltering them either. Genasi of all types are too alien compared to an aasimar to elicit sympathy or a sense of kinship.
Tieflings are the one race that garners the most suspicion from an aasimar, for those touched by the holy understand its calling and therefore can guess what sort of temptation those with unholy blood must hear.